The bacterial species Burkholderia pseudomallei and Burkholderia mallei, though genetically very similar, have divergent lifestyles. B. pseudomallei is a soil saprophyte and facultative pathogen, causing the disease melioidosis, while B. mallei is an obligate pathogen, the etiological agent of disease glanders. Melioidosis is mostly a disease of humans and animals of Southeast Asia and Northern Australia, where B. pseudomallei is endemic in the soils. Infection mainly occurs upon inhalation or aspiration of the organism, or through open wounds. Clinical manifestations of melioidosis can be asymptomatic, localized to virtually any organ, or disseminated, though the primary presentations are pneumonia and sepsis, where mortality rates are significant. Glanders is mainly an equine disease found in much of the world, except for North America, Europe and Australia, with transmission to humans occurring primarily through direct contact with animals and aerosols. Clinical manifestations of glanders in humans are similar to those of melioidosis. Both species of bacteria are intrinsically resistant to several antibiotics and both are potential bioterrorism agents, deemed by the U.S. Centers for Disease Control and Prevention Category B Select Agents, for which no human vaccine is available. As such, the rapid detection and identification of these species is essential for immediate appropriate patient therapy and epidemiological surveillance or forensic investigation.
Identification of B. pseudomallei and B. mallei and diagnosis of melioidosis and glanders currently depends on time-consuming culture of the organism. Confirmation by biochemical assays can add a week onto definitive species identification without guarantee of accuracy. However, rapid biochemical assays have resulted in misdiagnosis of melioidosis, a mistake not easily detected due to the myriad clinical manifestations of the disease, and the lack of vigilance for these organisms in non-endemic regions. Serologic assays can be erroneous for multiple reasons. Serologic assays are contingent on a delayed immune response, and are useful only in non-endemic areas, where seroconversion due to previous exposure is improbable. Antigen-specific assays, including direct immunofluorescent microscopy and latex agglutination, have proven to be rapid and sensitive, but are not as yet available commercially.